1. Field of the Invention
The present invention relates generally to a control circuit for a vehicle leveling system which properly adjusts the height of a vehicle body in response to changes therein.
2. Description of Relevant Art
A known type of vehicle leveling system incorporates a device, actuated by the pressure of fluid, which assists a suspension mechanism for always maintaining the height of a vehicle at a constant level, with the height of the vehicle body supported by the suspension mechanism being varied in accordance with changes in loads on the vehicle body. For a vehicle leveling system of this type, various control circuits are known which function to operate the vehicle leveling system to effect inherently required adjustments of vehicle height to maintain the aforesaid constant level, but to avoid operating the leveling system in response to changes in vehicle height which ordinarily occur during travel of the vehicle.
A recent exemplary control circuit for a vehicle leveling system of the aforesaid type is disclosed in U.S. Pat. No. 4,105,216. Such control circuit includes a detector which detects the vehicle height and generates a pair of signals (0, 0) when the vehicle height is above a predetermined range; a pair of signals (0, 1) when the height is within the predetermined height range; or a pair of signals (1, 1) when the height is below the predetermined height range, thereby controlling a vehicle leveling system to properly restore the vehicle height, when the signals (0, 0) or (1, 1) are generated, to be within the predetermined height range. More specifically, when either pair of signals (0, 0) or (1, 1) is generated, a delay timer circuit is operated through a NOT gate and/or an AND gate according to the combination of signals, so as to actuate the vehicle leveling system only after a delay time which is preset in the delay timer circuit has elapsed.
With the above-described arrangement, the control circuit determines, by comparing the delay time and a duration of the detected signal pair (0, 0) or (1, 1) indicating a change in the vehicle height, whether the detected signal pair is an ordinary one during travel or a particular one requiring an adjustment of vehicle height. If the duration of the detected signal pair (0, 0) or (1, 1) is shorter than the delay time, the control circuit functions to hold the vehicle leveling system in an inoperative condition.
Generally, the aforesaid vehicle leveling system, when provided on a passenger car, maintains the desired or proper vehicle height, thus improving the riding comfort and increasing the product value of the passenger car. It is also generally attempted to improve the riding comfort by enabling the control circuit to more finely adjust the vehicle height according to the changes in vehicle height. For example, the delay timer may be employed to delay the operation of the vehicle leveling system for a certain length of time, as described hereinabove.
However, technically conflicting demands arise with respect to a vehicle leveling system of the aforesaid type and its control circuit. One such demand resides in achieving a more accurate and precise vehicle height adjustment so as to increase the product value of a passenger car; while another demand is to simplify the vehicle leveling system and its control circuit so as to reduce the number of parts and elements as well as the manufacturing cost. In other words, it is desired to provide a more accurate, fine and advanced vehicle height adjustment while at the same time minimizing the expense and simplifying the construction with respect to the vehicle leveling system including the control circuit.
In view of the above considerations, the aforesaid known control circuit has a number of attendant disadvantages. Because the delay timer circuit includes an oscillator-operated hexadecimal binary counter, which fundamentally comprises four flip-flop circuits, it comprises a relatively complex and expensive digital circuit. Moreover, the necessary use of a plurality of such digital circuits results in a considerable increase in total cost. Further, the aforesaid control circuit is designed so as to function according to the combination of pairs of signals from a detector, thus resulting in complicated wiring and overall circuitry complexity. In addition, when a more complex and higher control is made by using such control circuits, for example, when an independent vehicle height adjustment is effected at each of the front and rear sides of an automobile according to respective changes in vehicle height or when vehicle height adjustments are effected at a plurality of points, there will naturally result further undesirable increases in manufacturing cost and circuitry complexity.
Due to the foregoing disadvantages attendant known circuitry, there has now developed a desideratum for a more simplified, reliable and low-cost control circuit for a vehicle leveling system which can operate favorably according to the complexity of actual change in vehicle height.
The present invention provides an improved control circuit for a vehicle leveling system which effectively fulfills the aforesaid desideratum.